712 



PHYSIOLOGICAL BASIS OF POL.AJRITY. II 



node and not from the first node behind the leaf.^ The reason for 

 this Hes probably in the fact that the dormant root bud in the second 

 node Hes in the path of the descending sap from the leaf, while the 

 root bud in the first node basally from the leaf lies above this path. 

 We notice generally that in a piece of stem suspended horizontally, 



Fig. 23. Showing that one node behind the leaf suffices for this inhibition of 

 the growth of roots in the buds situated apically from the leaf. 



possessing one apical leaf on the under side and two nodes basally 

 from the leaf, roots will grow out before they grow out in a similar 

 piece of stem possessing only one node basally from the leaf. 



7 Loeb, J., Bot. Gaz., 1917, bdii, 25. 



